1. Field of the Invention
The present invention relates to dispensers for delivering controlled amounts of fluids. More particularly, the invention relates to a metering dispenser for dispensing precisely controllable small amounts of adhesive to a workpiece.
2. Description of Background Art
A variety of devices adapted to dispense small amounts of fluid adhesives exists. For example, glue jars having a screw cap provided with an attached brush that protrudes downwards into the bottle, have long been known and used. Flexible, squeezable metal or plastic tubes having a small orifice sealed by a screw cap are widely used to dispense various types of adhesives, such as "model airplane" glue containing aromatic hydrocarbons, casein based wood glues, and the like.
One class of adhesives that has become increasingly popular for a wide variety of industrial, commercial and consumer applications is the cyanoacrylates. Cyanoacrylates, which are available as both relatively low viscosity fluids and thicker gels, produce adhesive bonds having a very high tensile strength. For that reason, adhesive bonds formed by cyanoacrylates typically utilize smaller amounts than other types of adhesives. Thus, cyanoacrylate adhesives often are packaged in smaller flexible tubes than are other adhesives, and require a little more finesse in applying adhesive to surfaces to be bonded, since usually only a very small amount of adhesive is required to optimize joint strength.
Besides the requirement for dispensing relatively small amounts of material, dispensers for cyanoacrylates must deal with the problem of clogging of the dispenser delivery orifice. Thus, tubes containing cyanoacrylates, as well as other types of adhesives, usually have a sealed bulkhead under a screw cap, which must initially be pierced with a pin or nail to permit adhesive to be expelled from the tube. After the required amount of adhesive has been dispensed by squeezing the tube, the cap is screwed back on the end of the tube to prevent the adhesive from drying out and hardening. However, owing to the flexibility and shape memory of the tube containing the adhesive, release of squeezing pressure on the tube often results in a re-expansion of the tube. This action draws air through the outlet orifice back into the tube. In the case of cyanoacrylates, oxygen and/or moisture in the air can thicken and harden adhesive within the tube, which must then be prematurely discarded, if the adhesive becomes too hard.
Since cyanoacrylate adhesives form almost instantaneous bonds between a wide variety of materials, including human skin, it would be desireable to provide dispensers for these adhesives that are so constructed as to prevent the possibility of accidental spilling, expelling or squirting adhesive from the dispenser.
Because of the considerations mentioned above, it would also be desirable to have a dispenser for cyanoacrylate adhesives that is capable of delivering small, precisely controllable amounts of adhesive, while eliminating spaces for air above or around adhesive remaining in the dispenser. Although the present inventors are unaware of the existence of any prior art metering dispensers specifically intended to address problems associated with the dispensing of cyanoacrylate adhesives, a number of prior art references disclose dispensers for metering controlled quantities of viscous materials such as dental compositions. These include the following United States patents:
Herold, et al, U.S. Pat. No. 4,479,781, Oct. 30, 1984, Dispenser For Metering Dental Compositions
Discloses a one-hand operated dispenser for metering dental compositions that comprises a casing for receiving the dental composition between a forward dispensing end and a plunger which is movably mounted within the casing. The plunger is moved forwardly by means of a threaded spindle which engages with a nut disposed on the rear casing end so as to be secured against rotation and axial movement. The thus formed assembly may be inserted into two bifurcated brackets of a generally U-shaped receptacle forming part of a manipulating member. The spindle is guided in the one bracket so as to be axially movable and non-rotatable, while the casing with the nut is mounted on the other bracket so as to be non-displaceable but rotatable. When the manipulating member is gripped, the casing may be turned between thumb and index finger such that the spindle is pushed forwards, whereby the dental composition exists from the dispensing opening.
The dispenser uses a threaded spindle having a longitudinally disposed flat held irrotational between the two arms of a bifurcated rear bracket forming part of a generally U-shaped receptacle forming part of a "manipulating member," i.e., a handle. A nut threadably holding the spindle is fastened to the rear end of the casing body, which has forward of the nut an annular groove that is held between the two arms of a bifurcated front bracket of the handle. The casing is rotated within the front bracket to cause the threaded spindle to advance into the casing, thereby causing a plunger driven by the front end of the spindle to expel fluid dental composition from the forward dispensing end of the casing.
Neumeister, et al., U.S. Pat. No. 4,560,352, Dec. 24, 1985, Dispenser For Metering Dental Composition
Discloses a one-hand operated dispenser for metering dental compositions that comprises a casing for accommodating the dental composition between a forward dispensing opening and a plunger which is slidable within the casing. The plunger is advanced by means of a threaded spindle which engages in a nut mounted at the casing rear end so as to be secured against rotation and axial displacement. The casing rear end is rotatably supported within a sleeve which in turn is detachably inserted in a handle. The sleeve is formed with an axially extending slot through which a finger is visible which is disposed at the rear end of the spindle. When the handle is gripped, the casing may be rotated between the thumb and index finger such that the spindle advances the plunger thereby urging the dental composition out of the dispensing opening. During the forward movement of the spindle the finger travels forwardly in the axially extending slot and indicates the level of the dental composition.
The dispenser uses a rotatable casing, as Herold '781, but uses a threaded spindle without a flat held irrotationally within in a sleeve attached to a handle, a finger protruding radially outward from the end of the spindle held longitudinally slidably but irrotationally within a longitudinally disposed slot in the sleeve.
Vlasich, U.S. Pat. No. 4,641,766, Feb. 10, 1987, Metering Dispenser For High Viscosity Compositions
Discloses a dispensing device including a hollow cylindrical body from which a high viscosity composition is discharged in precisely metered doses by a plunger rod longitudinally movable within the body. A series of projections are formed at equi-spaced, longitudinal intervals from each other on the plunger rod. A pair of parallel actuating arms pivotally mounted on the body extend along opposite sides of the plunger rod and are formed with a pair of teeth, respectively, projecting inward toward the rod. By depressing the arms, the teeth pivot into engagement with one of the projections to advance the plunger within the body to expel a desired amount of composition. In a preferred embodiment, advancement of the plunger rod through a precise distance is automatically controlled via contact between the teeth with stop surfaces formed on the next in-line projection.
Vlasich, U.S. Pat. No. 4,658,993, Apr. 21, 1987, Metering Dispenser For Viscous Compositions
Discloses a dispensing device which includes a hollow cylindrical body from which a high viscosity composition is discharged in precisely metered doses by means of a plunger rod longitudinally movable within the body. The plunger rod includes a series of thread segments formed at equi-spaced, angular intervals from each other to establish an exterior thread of constant pitch in threaded engagement with the body. Each segment has an abutment surface projecting from the surface of the plunger. By depressing a trigger mounted on the body into contact with an abutment surface aligned therewith, the plunger rotates through the angular interval and thereby advances through the body to expel a desired amount of composition. Disengagement of the trigger with the abutment surface automatically occurs as the abutment surface rotates to the end of the angular interval, out of contact with the trigger, causing the next in-line abutment surface to be indexed into alignment with the trigger to allow for successive doses.
British Patent No. 1,008,505, Quenzer, et al., Nov. 13, 1962, Cylindrical Container With Screw-In Spindle And Piston For Expelling The Contents Through A Frontal Opening
Discloses a cylindrical container for dispensing viscous materials which utilizes rotation of a knob attached to the rear end of a spindle threadingly engaged by a cap on the rear end of the cylinder to advance a piston contacted by the front end of the spindle, thereby expelling material from an opening in the front end wall of the cylinder.
German Patent No. 223,920, Jun. 26, 1985, Tube Filling Appliance
Discloses a tube filling Appliance for the dosage, filling and application of ointments or substances of similar viscosity in pharmaceutical dispensaries under sterile conditions that consists of a glass cylinder with a filler tube in which a piston can be moved by a feedscrew.
A handwheel attached to the end of the feedscrew is turned to move the piston forward. The device includes a stand that is equipped with a suction cup type of footing. The glass cylinder is laid in the stand affixed by a bayonet joint of the cap.
The tube to be filled (e.g., an aluminum tube for eye ointment) is pushed over the filler tube.
The present invention was conceived to provide an improved dispenser for metering small amounts of fluid material, the dispenser being particularly well adapted to dispensing cyanoacrylate adhesives.